Prestressed concrete structures



2 Sheets-Sheet 1 Filed Jan. 2'7, 1961 ATTORNEYS Nov. 16, 1965 J. J.CLOSNER 3,217,451

PRESTRESSED CONCRETE STRUCTURES Filed Jan. 2'7. 1961 2 Sheets-Sheet 2INVENTOR.

John J. Closner BY United States Patent 3,217,451 PRESTRESSED CQNCRE'IESTRUCTURES John J. Closner, New York, N .Y., assignor to The PreloadCompany, New York, N.Y. Filed Jan. 27, 1961, Ser. No. 85,324 7 Claims.(Cl. 52224) This invention relates to prestressed structures of concretesuch as tanks, domes, and the like, as Well as the method of constuctingthe same; and, in particular, to structures wherein the tensionedtendons are properly p0- sitioned and'covered by a protective coating.

Heretofore, the principal technique for prestressing concrete structureshas been to wrap and tension tendons, usually several layers of hightensile strength steel wires, strand or cable, about the outside surfaceof the structure and to cover each tendon layer with a protectivecoating of mortar to prevent corrosion. The application of an individualmortar coat over each tendon layer is not only an expensive operationbut also a time consuming one. Before the present invention when severallayers of tendons were used, it was necessary to apply one tendon layer,cover coat this layer with mortar and let the mortar set and hardenbefore applying the next tendon layer. In addition to the time lost bywaiting for the mortar to set, other slowdowns also result frominclement weather conditions since mortar cannot be readily applied invery cold or wet weather.

A further shortcoming of prior technique is that the successive coats ofmortar (which must be applied over each tendon layer) are usually notevenly finished due to the nature of the material and the methods ofapplying it. Therefore, since each mortar coat does not present an evenand true bearing surface for the succeeding tendon layer, sand or airpockets may form between the tendon and the previous mortar coat whenthe tendon layer is coated. These sand or air pockets act as reservoirsfor moisture and may cause corrosion of the steel tendons. Suchcorrosion is a very serious problem and the maintenance required toovercome it often dissuades against the use of prestressed reinforcedconcrete structures.

Accordingly, it is an object of the present invention to overcome suchdifiiculties by providing a structure and method of construction whichinsures proper spacing of the various layers of tendons and whichpermits the application of all the layers of tendons to be completedbefore any protective coating is applied.

It is a further object to provide a structure and method which issimple, more economical to use than the prior art methods andstructures, and which helps to reduce maintenance problems relating tothe corrosion of the tendons.

Although in the accompanying drawings a preferred embodiment of thepresent invention is shown and described in this specification, it is tobe understood that this is not intended to be exhaustive and limiting ofthe invention, but, on the contrary, it is chosen for the purpose ofillustrating the invention in order that others skilled in the art mayso fully understand the invention, its principals and the applicationthereof, that they may embody it and adapt it in numerous forms, each asmay be best suited to the requirements of the particular use.

In the drawings:

FIGURE 1 is a perspective view of a completed prestressed reinforcedconcrete tank in accordance with the present invention.

FIGURE 2 is a vertical sectional view through a portion of the wall ofthe completed tank showing the spacing of the various layers ofprestressing tendons.

FIGURE 3 is similar to FIGURE 2 but taken along the lines 33 of FIGURE 1and FIGURE 4 is a sectional view of a section of the wall taken alonglines 44 of FIGURE 1.

3,217,451 Patented Nov. 16, 1965 FIGURE 5 is a fragmentary perspectiveview of a section of the wall with the first tendon layer tensionedthereon.

FIGURE 6 is a view similar to FIGURE 5 with the first row of separatorsadded.

FIGURE 7 is a view similar to FIGURE 6 with the second tendon layeradded.

FIGURE 8 is a view similar to FIGURE 7 with the second row of separatorsin place.

FIGURE 9 is a view similar to FIGURE 8 with the third tendon layerapplied.

FIGURE 10 is a view similar to FIGURE 9 with a form in place prior topouring a protective coating about the tendon layers and separators.

FIGURE 11 is a view similar to FIGURE 10 with the protective coating inplace.

FIGURE 12 is a view similar to FIGURE 11 but of an embodiment wherein arow of separators are inserted between the wall and the first tendonlayer.

Referring to the drawings, and to FIGURE 1 in particular, a reinforcedconcrete tank 10, is shown, which has sidewalls 12, a dome top 14, and adome ring 16 for prestressing and supporting the dome. The sidewalls 12and the dome ring 16 have been wound with a series of high tensilestrength prestressing steel tendons over which has been applied aprotective coating of mortar.

The tendon and coating combination may best be understood by referringto FIGURES 2, 3, and 4. As shown therein, the sidewalls 12 are comprisedof a concrete core wall 18, a series of layers of high tensile strengthprestressing tendons 20, upright separator bars 22 and a protectivecover coating 24.

In constructing the tank 10, the core wall 18 is first formed and set inplace on a suitable foundation by means which are well known in the art.With the core wall 18 constructed, the first layer of prestressingtendons 20 are applied. These may be applied by wire winding apparatussuch as shown in US. Patent Nos. 2,372,060 and 2,364,- 696 or by anyother suitable means which are known to the art.

It is to be understood that tendon layer as used in this specificationdoes not require the tendons to be in intimate contact with each other.

After the first tendon layer was in place, the practice heretofore hasbeen to apply a protective coating of mortar over this layer. The mortarwas usually applied by spraying it with a mechanical coating apparatus.This first layer of mortar had to set and'harden before the next layerof wire could be applied. It was also necessary that the proper climaticconditions exist before applying the mortar coating. In very coldweather or in rain or snow it was not possible to apply the mortarcoating satisfactorily.

In distinction with the prior art methods the present invention does notrequire that the first tendon layer be coated with the mortar before thenext tendon layer is applied. As shown in FIGURES 5-11, all prestressingtendons are applied before cover coating. In carrying out the presentinvention in accordance with the illustrated embodiment of FIGURES 5-11,a row of upright separator bars 22a are spaced circumferentially aboutthe first tendon layer 2051 which is tensioned about the core wall 18.In actual practice, when using a high tensile strength A inch diametersteel wire as the prestressing tendon, separator bars one inch wide andinch thick have been found satisfactory. The second tendon layer 20b isapplied to the tank and prestressed over the first row of separator bars22 before a mortar coat is applied.

With the second tendon layer 20b in place, a second set of uprightseparator bars 22b are spaced over the second layer 20b and arranged onthe same radial line with the respective separators of the first row ofbars 22a. A third tendon layer 20c is then applied over the second rowof bars 22b. Additional alternate rows of bars 22 and tendon layers 20are applied as required with each succeeding row of separators radiallyaligned with the respective separators of the preceding rows. Thisradial alignment concentrates the bearing load of each tendon layer 20at each of the pressure points formed by the radial stack of separators.Thus, better design and construction control is possible.

It is to be understood that the number of tendon layers and thecorresponding number of rows of separators will be determined as amatter of design.

The circumferential spacing of the separators is dependent upon theradius of the tank wall. Each stack of separators may advantageously bespaced so that the second tendon layer is no more than tangential to thefirst layer midway between separators, thus insuring proper load bearingas well as permitting good protective coating of all the tendons.

After all the tendon layers and rows of separators are in place, theprotective coating 24 is preferably applied by placing a form 26 (asshown in FIGURE and pouring the coating 24 about the tendons. Where thenumber of tendon layers is small and the spacing permits, mechanicalspraying may be used.

Also with dome rings and the like, it will often be found to be moreeconomical and easier to obtain full coverage of the tendons bypreparing a form and pouring the cover coating.

While the cover coating will usually be a cement mortar, it is alsowithin the scope of the present invention to use other plasticmaterials.

In many cases, the finish of the core wall 18 is uneven and rough.Accordingly, as shown in FIGURE 12, in actual practice it usually isdesirable to place a row of separators 28 directly against the wall 18before the first tendon layer is applied and tensioned. Such anarrangement insures that the bearing and point load on the wall will befully concentrated at the separators. In addition, it is a furthersafeguard against sand or air pockets possibly forming between the corewall 18 and the first tendon layer when the protective coating isapplied.

The use of a row of separators 28 directly against the core wall servesto transfer the prestress tensile force of the series of tendon layersuniformly through the vertical extent of the first row of separators 28.This arrangement has the particular advantage of preventing a sawingcutting, or crushing of the concrete in the core wall.

In constructing a Wall using the row of separators 28, the same methodas described hereinbefore except that as an initial step the row ofseparators 28 is first positioned about the core Wall before the firsttendon layer a is applied.

I claim:

1. The method of prestressing a substantially cylindrical concrete tankstructure which comprises applying a first layer of a prestressingtendon about the structure, placing a first row of upright separatorscircumferentially spaced about the structure and adjacent to the firsttendon layer, applying at least two additional layers of prestressingtendons to the structure with another row of upright separatorspositioned between each two additional layers of prestressing tendons,the separators in each row being radial- 1y aligned with the respectiveseparators in each other row, and applying a cover coat of protectivematerial over the tendons and the upright separators.

2. A substantially cylindrical concrete tank structure comprising anannular core wall prestressed with a first layer of a high tensilestrength tendon, a first row of upright separators circumferentiallyspaced about the Wall and contacting the first tendon layer, a secondlayer of prestressing tendon tensioned about the wall and over the firstrow of separators, additional alternate rows of separators and tendonlayers, said separators in each row being in radial alignment with therespective separators in each other row, and a protective cover coatingover the layers of prestressing tendons and the upright separators.

3. The method of prestressing a substantially cylindrical concrete tankstructure which comprises applying a row of upright separatorscircumferentially spaced about the structure, tensioning a first layerof a prestressing tendon about the structure and over the first row ofseparators to achieve a desired elongation of said tendon layer,applying a second row of upright separators circumferentially spacedabout the structure and over said first tendon layer and radiallyaligned with the respective separators of said first row of separators,tensioning a second tendon layer about the structure and over the secondrow of separators to achieve a desired elongation of said second tendonlayer, and applying a cover coat of protective material over the tendonlayers and the upright separators.

4. The method of claim 3 wherein the upright separators of the first roware spaced apart so that the chords formed by the first tendon layer aretangent to the concrete structure.

5. The method of claim 3 wherein the upright separators of the first roware spaced apart so that the chords formed by the first tendon layer arespaced from the concrete structure.

6. A substantially cylindrical concrete tank structure comprising anannular core prestressed with a first layer of a high tensile strengthtendon tensioned to a desired elongation about the core, a first row ofupright separators circumferentially spaced about the core and betweenthe core and said first tendon layer, a second row of upright separatorscircumferentially spaced about the structure and over said first tendonlayer and radially aligned with the respective separators of said firstrow, a second tendon layer tensioned about the core and over the secondrow of separators, a protective cover coat over the tendon layers andthe separators.

7. A substantially cylindrical concrete tank structure as defined inclaim 6 wherein the cover coat is a cementitious material.

References Cited by the Examiner UNITED STATES PATENTS 2,031,057 2/1936Mitchell 138-176 2,637,895 5/1953 Blaton 50-135 2,662,555 12/1953 Hirsh138-176 FOREIGN PATENTS 1,222,543 I/ 1960 France.

367,743 2/1932 Great Britain.

JACOB L. NACKENOFF, Primary Examiner.

WILLIAM I. MUSHAKE, HENRY C. SUTHERLAND,

Examiners.

2. A SUBSTANTIALLY CYLINDRICAL CONCRETE TANK STRUCTURE COMPRISING ANANNULAR CORE WALL PRESTRESSED WITH A FIRST LAYER OF A HIGH TENSILESTRENGTH TENDON, A FIRST ROW OF UPRIGHT SEPARATORS CIRCUMFERENTIALLYSPACED ABOUT THE WALL AND CONTACTING HE FIRST TNEDON LAYER, ASECONDLAYER OF PRESTRESSING TENDON TENSIONED ABOUT THE WALL AND OVER THEFIRST ROW OF SEPARATORS, ADDITIONAL ALTERNATE ROWS OF SEPARATORS ANDTENDON LAYERS, SAID SEPARATORS IN EACH ROW BEING IN RADIAL ALIGNMENTWITH THE RESPECTIVE SEPARATORS IN EACH OTHER ROW, AND A PROTECTIVE COVERCOATING OVER THE LAYERS OF PRESTRESSING TENDONS AND THE UPRIGHTSEPARATORS.